Communication Method, CP Device, and NAT Device

1. A network device, applied to a control plane (CP) device in a communications system in which a CP and a user plane (UP) are separated, the network device comprising: at least one processor; and one or more non-transitory memories coupled to the at least one processor and storing programming instructions, wherein the at least one processor is configured to execute the programming instructions to cause the network device to: assign a first Internet protocol (IP) address to a user; send the first IP address to a network address translation (NAT) device; receive information about the user from the NAT device, wherein the information about the user comprises a correspondence among the first IP address, a second IP address, and a port block, wherein the second IP address is a public network IP address that is assigned by the NAT device to the user based on the first IP address, and the port block comprises at least one port number that is assigned by the NAT device to the user; and send an accounting packet to a remote authentication dial in user service (RADIUS) server, wherein the accounting packet comprises the first IP address and the second IP address and the port block.

2. The network device according to claim 1, wherein the first IP address comprises at least one of a private network Internet protocol version 4 (IPv4) address or an Internet protocol version 6 (IPv6) address.

3. The network device according to claim 1, wherein the communications system comprises a gateway system, and the gateway system is a broadband network gateway (BNG) system or a broadband remote access server (BRAS) system.

4. The network device according to claim 1, wherein the at least one processor is further configured to execute the programming instructions to cause the network device to: receive a port block set from the RADIUS server, wherein the port block set comprises the port block; and send the port block set to the NAT device.

5. The network device according to claim 1, wherein the at least one processor is further configured to execute the programming instructions to cause the network device to: when the user is offline, send a delete message to the NAT device, wherein the delete message indicates the NAT device to delete the information that is about the user and that is stored in the NAT device; and delete the information that is about the user and that is stored in the CP device.

6. The network device according to claim 1, wherein the NAT device comprises an active NAT device and a standby NAT device, each of which is a reserve one to the other, and the at least one processor is further configured to execute the programming instructions to cause the network device to: receive the information about the user from the active NAT device.

7. The network device according to claim 6, wherein the at least one processor is further configured to execute the programming instructions to cause the network device to: send the information about the user to the standby NAT device.

8. The network device according to claim 6, wherein the at least one processor is further configured to execute the programming instructions to cause the network device to: when the active NAT device is in a faulty state, send a first update message to the standby NAT device, wherein the first update message indicates the standby NAT device to increase a route priority corresponding to the second IP address.

9. A network device, applied to a network address translation (NAT) device, the network device comprising: at least one processor; and one or more non-transitory memories coupled to the at least one processor and storing programming instructions, wherein the at least one processor is configured to execute the programming instructions to cause the network device to: receive, from a control plane (CP) device in a communications system in which a CP and a user plane (UP) are separated, a first Internet protocol (IP) address that is assigned by the CP device to a user; assign a second IP address and at least one port number to the user based on the first IP address, wherein the second IP address is a public network IP address; and send information about the user to the CP device, wherein the information about the user comprises a correspondence among the first IP address, the second IP address and a port block, and the port block comprises the at least one port number.

10. The network device according to claim 9, wherein the at least one processor is further configured to execute the programming instructions to cause the network device to: assign the port block to the user, wherein the port block comprises at least one port number; and send the port block to the CP device.

11. A communications system in which a control plane (CP) and a user plane (UP) are separated, the communications system comprising a CP device and a NAT device, wherein the CP device is configured to: assign a first Internet protocol (IP) address to a user; send the first IP address to a network address translation (NAT) device; receive a second IP address from the NAT device, wherein the second IP address is a public network IP address that is assigned by the NAT device to the user based on the first IP address; and send an accounting packet to a remote authentication dial in user service (RADIUS) server, wherein the accounting packet comprises the first IP address and the second IP address; and wherein the NAT device is configured to: receive the first IP address from the CP device; assign the second IP address to the user; and send the second IP address to the CP device.

12. The communications system according to claim 11, wherein the first IP address comprises at least one of a private network Internet protocol version 4 (IPV4) address or an Internet protocol version 6 (IPv6) address.

13. The communications system according to claim 11, wherein the communications system comprises a gateway system, and the gateway system is a broadband network gateway (BNG) system or a broadband remote access server (BRAS) system.

14. The communications system according to claim 11, wherein the accounting packet further comprises a port block, and the port block comprises at least one port number that is assigned by the NAT device to the user, and wherein the CP device is further configured to: receive information about the user from the NAT device, wherein the information about the user comprises a correspondence among the first IP address, the second IP address, and the port block.

15. The communications system according to claim 11, wherein the CP device is further configured to: receive a port block set from the RADIUS server, wherein the port block set comprises the port block; and send the port block set to the NAT device.

16. The communications system according to claim 11, wherein the CP device is further configured to: when the user is offline, send a delete message to the NAT device, wherein the delete message indicates the NAT device to delete information that is about the user and that is stored in the NAT device; and delete the information that is about the user and that is stored in the CP device.

17. The communications system according to claim 11, wherein the NAT device comprises an active NAT device and a standby NAT device, each of which is a reserve one to the other, and the CP device is further configured to: receive information about the user from the active NAT device.

18. The communications system according to claim 17, wherein the CP device is further configured to: send the information about the user to the standby NAT device.